摘要:

Major mortality events in marine mammal populations have become a feature of recent years and their causes have been much debated. Here we review the investigations that have been made to date into the 1988 seal epizootic in the North Sea region, the 1990-1992 striped dolphin epizootic in the Mediterranean Sea, and the recent spate of sperm whale strandings in the northeastern Atlantic. We consider the evidence for multifactorial causality in these events and the problems inherent in determining causes. The patterns of disease seen in both the phocine distemper virus and the dolphin morbillivirus precipitated events suggest complex underlying aetiologies with changes in hosts and (or) marine environment, with significant implications for the conservation and management of marine mammal populations. The sperm whale strandings are used to illustrate the difficulty of investigating or even detecting such events in marine mammal populations.

ISSN:1208-6053    

DOI:10.1139/a97-004

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Literature on the long-range atmospheric transport of both anthropogenic and naturally occurring mercury (Hg) to terrestrial and aquatic ecosystems was reviewed for the purpose of assessing the quantitative importance and environmental significance of the anthropogenic emissions. The weight of evidence, comprising many different kinds of data that corroborate each other independently, supports the following conclusions. (i) Approximately 5000 t of anthropogenic Hg are introduced into the atmosphere every year, both by direct emission from sources of pollution and by reemission of previously deposited Hg from diffuse secondary sources in the environment. The primary emissions ( 4000 t) result from various human activities, especially the combustion of fossil fuels (notably coal) and solid wastes. Natural emissions amount to about 2000 t/year. (ii) Although some of the annual anthropogenic Hg output (about half the quantity emitted by primary sources) is deposited near its point sources, the rest (a total of 3000 t) is subject to transport over great distances by atmospheric circulation, resulting in measurable contamination of terrestrial and aquatic environments and organisms up to several thousand kilometers from the points of origin. Indeed, a number of remote ecosystems receive most of their Hg input from the atmosphere. (iii) The available evidence supports the generally accepted conclusion that the Hg enrichment commonly seen in the uppermost horizons of sediment cores from remote lakes is due primarily to contamination by airborne anthropogenic Hg in the recent past, rather than postdepositional redistribution of Hg. Although postdepositional alteration may result in detectable remobilization of sedimentary Hg, its effects on total Hg profiles in lake sediment cores have been found, thus far, to be negligible. (iv) Atmospheric transport of anthropogenic Hg to aquatic and terrestrial ecosystems is a cause for concern, as the Hg is accumulating, to a greater or lesser extent, in organisms (e.g., fish in remote lakes). Moreover, the Hg is associated with, and interacts with, other by-products of fossil fuel combustion, including the strong acids responsible for acid precipitation. The acids aggravate the effects of Hg pollution by furthering the accumulation of methyl Hg in fish inhabiting ill-buffered lakes. Contamination of the atmosphere with Hg and associated pollutants is a serious international problem that calls for reduction or elimination of emissions.

ISSN:1208-6053    

DOI:10.1139/a97-005

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

Risk assessment and management have become central to many health and environmental issues in recent years. Despite high expectations for the applications of science to identify and manage risks, many of these issues remain controversial. Some of the foundations of risk assessment and management are explored and needs for improvement are identified. Inputs from models, data, and uncertainty analyses are reviewed and goals for risk assessment, management, and communication are considered. Ultimately a better understanding of the strengths and limitations of these processes, primarily by the specialists and decision makers, is a prerequisite to more effective involvement of affected stakeholders in risk management. Unless some better basic understanding is achieved, public expectations and demands for risk management are likely to remain unachievable.

ISSN:1208-6053    

DOI:10.1139/a97-006

出版商:NRC Research Press    

年代:1997

数据来源: NRC

摘要:

We utilize literature surveys to examine the relationship between establishment of exotic species and human or natural disturbances of ecosystems. Of the 133 papers published in 10 ecological journals between 1993 and 1995, 63 reported on field studies involving 299 and 103 successful, nonredundant plant and animal introductions, respectively. Invasions of terrestrial ecosystems dominated (>>97%) the surveyed literature. Disturbance was associated with establishment of exotic species in 56% of these studies, though its importance differed among papers describing plants (68%) and animals (28%). Plants species (86%) were significantly more dependent on disturbance for establishment than were animals (12%). However, animals and plants that were dependent on disturbance for establishment were almost equally dependent (58 versus 68%) on it for range expansion. In a second survey, 402 plant and 103 animal taxa were identified that explicitly linked establishment of exotic species to disturbance. Human activities were attributed with establishment of species in 97 and 57% of these cases, respectively. Common mechanisms associated with establishment of exotic animals included ballast water discharge, intentional releases, and residential development. Establishment of exotic plants was associated with animal activities (e.g., grazing, seed introduction), soil disturbance, forestry, fire, agriculture, and human activities. In contrast to invasions theory, our survey indicates that the association between establishment and spread of exotic species and disturbance ought not be assumed a priori. Some animals repeatedly invade new habitats once geographic barriers are circumvented, indicating that communities may be more receptive to exotic species than previously acknowledged. By contrast, introduced plants established most often in disturbed habitats.

ISSN:1208-6053    

DOI:10.1139/a97-007

出版商:NRC Research Press    

年代:1997

数据来源: NRC